Metal injection molding is a simple, cost-effective method that has widely been used to mold parts weighing less than 250 grams. This process has been used to inexpensively manufacture a myriad of components used in many different industries, such as automotive, firearms, and medical industries. Generally, metal injection molding includes four basic steps, namely, mixing fine metal powders with a binder to formulate a feedstock, molding the feedstock in an injection molding machine to form a green part, debinding the binder from the green part to produce a brown part, and sintering the brown part to form the component.
During sintering, the brown part is subjected to temperatures of at least about 2200° F. and may be as high as about 2800° F. for some iron-based alloy parts. When the brown part is exposed to such temperatures, it may become soft and susceptible to deformation. For small parts, such as those weighing less than 250 grams, the gravitational forces exerted on the part are relatively small and thus, do not cause the part to become structurally distorted. Thus, metal injection molding is an ideal manner by which to inexpensively produce small parts. However, when large parts, e.g. parts larger than 250 grams, are subjected to sintering temperatures, portions of the part may sag under its own weight. This may be particularly true when the large part includes walls that form a cylindrical section, such as in a flowbody. In such a case, the walls may cave inward or one part of the wall may, due to gravity, pull downward more than another part of the wall. In other cases, the large part may, in addition to having a cylindrical section, include side pieces formed thereon which, during sintering, may draw the wall downward as well. As a result, metal injection molding conventionally has not been used to produce large parts.
Thus, there is a need for a methods and tools that may be used for metal injection molding of parts of all sizes, including parts larger than 250 grams. It is also desirable for the methods and tools to be relatively inexpensive to use and produce. Moreover, it is desirable for the tools to be reusable. The present invention addresses one or more of these needs.